If \(A=\{x\in\mathbb{N}:x\le25,\ x\text{ is prime}\}\) and \(B=\{x\in\mathbb{N}:x\le25,\ x\text{ is odd}\}\), what is \(B-A\)?
Answer and explanation
Correct answer: \(\{1,9,15,21,25\}\)
List the odd natural numbers not exceeding 25: \(B=\{1,3,5,7,9,11,13,15,17,19,21,23,25\}\). The primes among them are \(3,5,7,11,13,17,19,23\), which form \(A\). Set difference \(B-A\) keeps elements of \(B\) that are not in \(A\). Therefore, it contains 1 and the odd composite numbers 9, 15, 21, and 25, giving \(\{1,9,15,21,25\}\).
Frequently asked questions
What is the correct answer to this question?
\(\{1,9,15,21,25\}\)
Why is this the correct answer?
List the odd natural numbers not exceeding 25: \(B=\{1,3,5,7,9,11,13,15,17,19,21,23,25\}\). The primes among them are \(3,5,7,11,13,17,19,23\), which form \(A\). Set difference \(B-A\) keeps elements of \(B\) that are not in \(A\). Therefore, it contains 1 and the odd composite numbers 9, 15, 21, and 25, giving \(\{1,9,15,21,25\}\).
Which subject and chapter does this question cover?
This is a Class 10 Mathematics question. Chapter: Sets. Topic: Operations on Sets (Union, Intersection, Difference).
